1. Field of the Invention
This invention relates to sensors. In particular, there is a sensor that can measure the relative displacement between two rotating shafts. The sensor can be used to sense the amount of torque applied to a steering wheel in a vehicle as well as the position of the steering wheel.
2. Descripton of the Related Art
Various devices and methods of dealing with the design of steering wheel sensors are known.
Examples of prior art steering wheel sensors are shown in U.S. Pat. Nos. 5,763,793 and 5,837,908. The devices described in these patents measure torque applied to a steering wheel. Unfortunately, these devices are very expensive and difficult to manufacture because of the large number of rotating contacts needed to collect the electrical signal and then to bring the electrical signal off the rotating member to a connector. For example, the device of the ""908 patent requires 16 electrical contacts. Since, the contacts are made of a precious metal typically high in palladium, they are very expensive and quickly add cost to the device.
The automotive industry has been focusing on electrical assist power steering for vehicles. The electrical assist power steering unit is an electrical motor attached to the steering linkage that operates when assist is required. A large amount of torque on the steering wheel occurs at low speed operation or during parking. The electrical assist power steering is generally not needed during high speed operation such as during highway driving. The major advantages of electrical assist power steering are first, that it only operates during the short time of turning and is inoperative the rest of the time and second that it is simpler to manufacture. In a hydraulic power steering system, the power steering pump is always being turned by the engine and represents an energy drain on the motor all the time even though steering is only performed during a small percentage of the total time a car is operated. An electrical assist power steering system requires sensing of torque applied to the steering wheel. The torque indicates how much force the operator is exerting to move the wheel. The output signal from a torque sensor is fed into a control unit which controls the electrical motor of the assist unit. When the torque sensed is high, the assist applied to the steering linkage will be high. When the torque sensed is low, the assist applied to the steering linkage will be low. Unfortunately, the current electrical assist power steering units tend to overshoot or overcompensate once it is activated. The operator will tend to have to counter compensate a small amount with the wheel during operation so that the wheel does not turn beyond the desired turning point. It is desirable to provide an advanced electrical assist power steering system with better operator ergonomics that feels the same during operation as the current hydraulic power steering systems. In order to accomplish this, the control unit needs precise torque information. With a precise torque sensor, the control unit can operate in various modes. For example, when the steering wheel rotation is reversed, the rotational position sensor can sense the reversal and the electric motor can be reversed before a large reverse torque is built up on the wheel and felt by the operator. This faster motor reversal leads to better operator ergonomics.
In general, a sensor that measures the relative displacement between two rotating shafts has useful applications in the areas of industrial machinery, aerospace, electrical power generation and transportation.
There is a current unmet need for precise steering wheel torque sensor that is readily manufacturable at low cost. Additionally, there is a current unmet need for a sensor to measure the relative displacement between two rotating shafts.
It is a feature of the invention to provide a steering wheel sensor that can sense torque applied to the steering wheel of a vehicle and the rotary position of the steering wheel.
Yet, another feature of the invention is to provide a torque sensor for measuring the torque applied to a first and second shaft connected by a torsion bar. The sensor includes a housing having apertures at each end thereof. The shafts pass through the housing. A rotor is located in the housing and connected to the first shaft. The rotor has a top surface, a bottom surface and a side surface. The rotor further has a first and second contactor located on the bottom surface and a first and second conductive track located on the side surface. The conductive tracks are electrical contact with the first and second contactors. A rotating disc is connected to the second shaft. The disc has a top surface and a bottom surface. A first and second resistive track are disposed on the top surface of the disc. The first and second contactor contact the resistive tracks. A third and fourth contactor are located in the housing and are in electrical contact with the conductive tracks. A first and second electrical terminal are located in the housing and are electrically communicated with the third and fourth contactors to provide an electrical signal indicative of the torque on the shafts to an external electrical circuit.
The invention resides not in any one of these features per se, but rather in the particular combination of all of them herein disclosed and claimed. Those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. Further, the abstract is neither intended to define the invention of the application, which is measured by the claims, neither is it intended to be limiting as to the scope of the invention in any way.